The invention relates to a photosensitive member which may be used in an electrophotographic copying process.
A photosensitive member used for an electrophotographic copying process usually comprises zinc oxide, amorphous selenium or organic photoconductor (OPC). Usually, the photosensitive member is formed as a two-layer structure having a photosensitive layer formed of a material such as described above deposited on an electrically conductive support, or alternatively a three-layer structure in which an insulating support carries an electrically conductive layer, on which a photosensitive layer is formed. However, it is essential that the photosensitive member comprises at least an electrically conductive layer and a photosensitive layer. It is usually formed as a drum or an endless belt.
Considering a copying process which utilizes a photosensitive member, there are a number of problems. By way of example, during a charging step, it is only necessary that only a surface region of the photosensitive member which corresponds to an effective image portion of the original which is to be copied be charged. However, in practice, it is too late to initiate the charging step at the time the leading edge of the region of the photosensitive layer corresponding to the effective image area moves into a charger. It is also difficult to achieve an accurate coincidence between the initiation of the charging step and the movement of such region into the charger. For these reasons, the charging step is initiated before the leading edge of the region corresponding to the effective image area moves into the charger. This results in other portions of the photosensitive member other than the region corresponding to the effective image area to be charged unintendedly, causing a subsequent toner deposition and forming a solid black area thereon. In other words, these portions effectively function as part of the photosensitive member though undesirable. This also causes an increased loading during a developing and a cleaning step, requiring an increased use of toner. To accommodate for this, there has been a proposal to eliminate the charge on these portions of the photosensitive member other than the region corresponding to the effective image area as by irradiation from a quenching lamp, for example. However, the provision of such apparatus results in a complex arrangement of the copying machine.
An endless belt essentially comprising an organic photoconductor is known and is commonly referred to as an OPC photosensitive belt, which comprises an insulating support formed of polyester film carrying a conductive aluminium layer thereon, on which an OPC photosensitive layer is formed to provide a three-layer construction. When such photosensitive member is used, it is essential that the conductive layer be connected to the electrical ground. Hence, the conductive layer is partly exposed outside the surface photosensitive layer for contact with a brush for electrical connection with the ground. A variety of techniques are proposed to provide an electrical connection with the ground. Presently, the use of a brush is considered to be most favorable in that it is inexpensive and provides a compact structure.
However, the brush technique achieves the electrical connection with the ground by disposing a metal or carbon brush in sliding contact with the exposed portion of the conductive layer of the rotating OPC photosensitive belt, so that there arises the problem of the conductive layer being abraded. The conductive layer is normally formed by evaporation of aluminium or like material, and has a reduced thickness on the order of 400 to 700 A. Hence, as a result of sliding contact of the brush therewith over a prolonged period of time, the conductive layer becomes excessively abraded, causing a failure of the electrical connection with the ground. In certain instances, the insulating support may be exposed in the three-layer construction, causing the exposed insulating layer to be charged to cause a toner deposition thereon.